I've never seen it being mentioned directly, but from what I can tell GW Tau ships look this way because their design was heavily inspired by medieval chinese explorer ships (treasure ships?):

Not only are they both similar in desing being excessively big, bulky and possess a grace of a brick but they were also built with the same purpose - as first big attempts to explore what laid beyond their civilization's reach, more situated for scientific expeditions than combat.

Literally the sourcebook that the FW rules for the Tau are found. Tau don't warp in the normal way. The Battlefleet Gothic Tau Codex, the one specifically for Tau. The most direct quote as evidence (I was certain there was a direct statement that said essentially that by streamlining hull design they could dive deeper in the warp than they'd ever thought before) is from the Castellan class escort description:

"Like the other vessels designed during the Kor‟or‟vesh initiative, its unique hull design allows for considerably longer-range operations compared to its predecessor."

There's also this, from page 157(?): "They would have to bend the full ability, resources and technological prowess at the Empire‟s disposal to the task of creating a completely new range of vessels designed from the outset as warships with a level of redundancy, efficiency and dive range that were beyond the limits of current starship construction techniques."

As well, in the original BFG source for the Tau (BFG Armada), it specifically says that they extend the gravitic sheath into a wing shape. Kor'Or'Vesh vessels are obviously rather more wing-shaped than their initial vessels. "By carefully angling their descent toward the Warp and extending the field generated by the gravitic drive into a wing, shaped to hold the vessel down a Tau vessel could extend the duration of the dive considerably."

Rolepgeek wrote:Literally the sourcebook that the FW rules for the Tau are found. Tau don't warp in the normal way. The Battlefleet Gothic Tau Codex, the one specifically for Tau. The most direct quote as evidence (I was certain there was a direct statement that said essentially that by streamlining hull design they could dive deeper in the warp than they'd ever thought before) is from the Castellan class escort description:

"Like the other vessels designed during the Kor‟or‟vesh initiative, its unique hull design allows for considerably longer-range operations compared to its predecessor."

There's also this, from page 157(?): "They would have to bend the full ability, resources and technological prowess at the Empire‟s disposal to the task of creating a completely new range of vessels designed from the outset as warships with a level of redundancy, efficiency and dive range that were beyond the limits of current starship construction techniques."

As well, in the original BFG source for the Tau (BFG Armada), it specifically says that they extend the gravitic sheath into a wing shape. Kor'Or'Vesh vessels are obviously rather more wing-shaped than their initial vessels. "By carefully angling their descent toward the Warp and extending the field generated by the gravitic drive into a wing, shaped to hold the vessel down a Tau vessel could extend the duration of the dive considerably."

Is that sufficient?

Here's the thing. I have two ideas as to why there are these two seperate design schools for the Tau. first: These two stages in ship design are two AGES of ship design. the Kor'Or'Vesh designs are later and come with more knowledge than the designs of the Kor'Vattra, and are therefore more efficient. the other thing i can think of is that this was the result of something like what the US military does when it needs new stuff: hold a contest/competition. Like with the JSF project, Boeing and Lockheed Martin put forth two designs for the same purpose, and yet they were very different designs. the same might apply here, in that the worlds of the first age of Expansion (Including T'au) designed the Kor'Or'Vesh ships and the worlds of the second stage of expansion (Fal'Shia, Vior'La etc) created the Kor'Vattra ships. One fulfilled the natural ascetic common throughout the Tau because they could, the other had to basically design it for utilitarian purposes because they're already facing down Orks, not to mention the first scouts are coming back with reports of the Imperium. They don't have the time for Aesthetics, they needed a design and they put one out.

Me personally? Kor'Vattra all the way. I love my Explorer class, i thought it had this nice classic sci-fi feel to it that I associated with the Tau's infantry. Nevertheless, I hope both types are in the game, therefore we get the two/three classes of battleship, 6-7 classes of cruiser, and 4-5 classes of escort.

All of our failures fuel our success in the bloody and visceral weather game of chess.

If I remember right, Kor'Vattra ships were developed during and after Damocles Crusade. Not certain on that point, but yeah.

They also are designed for almost purely military use. I mean, obviously not the Emissary, but the rest are essentially purpose-built, as compared to Kor'Or'Vesh ships which were simply the first effective forays, and amounted to a merchant marine. Warp, the Merchant class was literally called such, and formed the bulk of Tau navies as soon as it was decent.